Sulphur dioxide is a gas formed by oxidation of materials containing sulphur, such as coal, oil, natural gas, industrial and domestic waste and peat. Sulphur dioxide can also be produced as a residual product in chemical processes, such as for instance in metallurgical processes. Usually, emitting large quantities of sulphur dioxide into the atmosphere is not allowed, and therefore some kind of cleaning is necessary. One example is flue gas cleaning in power plants and other combustion plants. The flue gas generated in the combustion process in such plants is usually cleaned by, inter alia, absorption of sulphur dioxide in an absorption liquid. The absorption liquid may contain, for instance, water and one or more of the substances lime, limestone, dolomite, sodium hydroxide solution and similar substances, which are suitable for absorption of sulphur dioxide.
WO 03/004137 discloses a method and a device for removing sulphur dioxide from a gas. In the method, the flue gas flows upwardly through an apertured plate having a flowing layer of an absorption liquid thereon. The absorption liquid flowing over the top surface of the apertured plate is collected and made to flow downwardly into a container. The flue gas to be cleaned firstly flows through a contact zone, where it is contacted with the absorption liquid flowing downwardly from the apertured plate, and secondly flows upwardly through the apertured plate.
U.S. Pat. No. 5,620,144 discloses a wet scrubber for removing sulphur dioxide from a process gas. The wet scrubber comprises a vertical tower in which a number of atomization nozzles are arranged for spraying of absorption liquid for the removal of sulphur dioxide from a process gas flowing through the scrubber.
It is difficult to determine the sulphur dioxide removal efficiency of such scrubbers according to prior art.